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Treatment is part of a total effort to contain the spread of most infectious diseases, from gonorrhea to tuberculosis. Most experts assumed that would apply to HIV as well—that treating people with antiretroviral therapy and lowering their HIV viral load would reduce the risk of transmission to others—but definitive evidence has been lacking.

Last year, a landmark National Institutes of Health clinical trial finally provided spectacular proof—a 96% reduction in new infections—of the preventive potential of treatment.

Myron “Mike” Cohen, a researcher at the University of North Carolina at Chapel Hill who led the study, said the results from an interim analysis of the study’s 1763 couples (where one was infected with HIV and the other was not) were so conclusive that the findings were made public before the trial’s completion.

There were 29 cases of HIV transmission between the partners, and “only one came from a person who was receiving [standard] therapy” of antiretroviral drugs, Cohen said. “We were reducing HIV transmission by 96% or more.”

Myron “Mike” Cohen
[All photos by Bob Roehr for AAAS]

Cohen led off a forum on “Treatment as Prevention” held at AAAS on 24 July, in conjunction with the XIX International AIDS Conference. The event was cosponsored by Science, Science Translational Medicine, the HIV Medicine Association, and the Center for Global Health Policy.

The NIH study has stimulated discussion on the role of treatment as one element in the toolbox of HIV prevention options, experts at the forum suggested.

“We probably cannot treat our way out of this epidemic,” Cohen acknowledged, noting that an HIV vaccine remains a key missing piece. But treatment combined with other preventive tools such as behavioral changes and early testing, he and others said, can act as “a bridge to the future” when a vaccine might become available.

“The [NIH] trial was something of a game-changer in the decision-making process” for HIV policy in New York City, said Blayne Cutler, who directs the city’s HIV prevention efforts. Starting treatment early “appears to be a very strong win-win” for personal medicine and public health, she said, as it improves clinical outcomes for the patient while reducing ongoing transmission of the virus.

The city has long offered HIV tests to all, regardless of an individual’s perceived risk for acquiring the virus, and linked people to care if they were HIV-positive. Last December, Mayor Michael Bloomberg announced the recommendation to offer antiretroviral therapy immediately upon a person’s diagnosis, rather than wait until his or her disease progressed and immune system declined.

HIV treatment guidelines over the past 15 years have consistently moved in the direction of earlier initiation of therapy. Newer antiretroviral drugs are more potent, easier to use, and have fewer side effects. The negative effects of delaying treatment also have become better understood, as recent studies demonstrate the effects of the virus’ ongoing replication and its connections to other conditions such as heart disease.

Studies have shown that people who know they are HIV-positive are more likely to practice safer sex than those who do not know their status. Also, HIV viral load correlates with risk of transmission; the lower the viral load, the lower the risk of transmission to others.

Once treatment is started, the goal is to suppress HIV viral load below the level of detection. Only 28% of persons believed to be infected with HIV in the U.S. are on treatment and have an undetectable viral load. Cutler said New York City does better, with an estimated 39% in treatment with an undetectable viral load. She attributes the difference to an integrated and supportive system of care.

San Francisco is the only other jurisdiction in the U.S. that has adopted a similar policy of immediate access to antiretroviral therapy. Money is a principal reason. Thousands of persons in the U.S. are on waiting lists to join the AIDS Drug Assistance Program in their state and begin treating their more advanced disease.

International perspectives

John Blandford

At the same time, fewer than half of the persons who should be on therapy in the developing world are receiving it. The President’s Emergency Plan for AIDS Relief is the U.S. government’s international AIDS effort that targets countries hardest hit by the epidemic, primarily in sub-Saharan Africa. But the recession has meant “a rapid slowing in the growth of global health resources,” said John Blandford, an economist focusing on HIV at the U.S. Centers for Disease Control and Prevention.

“Societal cost savings from averted negative outcomes are estimated at 59% of total treatment program costs in 2012,” Blandford said, and treatment may be considered “highly cost-effective” under World Health Organization guidelines.

The impact of treatment can be seen already in places such as the South African province of KwaZulu-Natal, Cohen said, where population data show that “for every 10% increase in antiviral therapy, you see a 2% fall in new cases of HIV.”

Models of an accelerated treatment scale-up in Kenya, Blandford said, found that costs would be greatest in the initial few years of the program but would then level off for the rest of the decade. “The next decades are where you really start to see the savings,” he explained. But the models also show that a lower level of treatment would result in a larger epidemic and hence greater costs over the longer term.

Challenges to Care

Dázon Dixon Diallo

From the risk of infection to adherence to treatment, “everything about HIV begins and ends with behavior,” said Dázon Dixon Diallo. She is the president of SisterLove, which runs HIV-oriented women-empowerment programs in Atlanta and South Africa.

“I don’t mean that just for the individual…who we eventually want to get undetectable and non-transmitting,” Diallo said. “But we are also talking about the behavior of communities” including society, governments, and industry.

One challenge in the South, where the U.S. HIV epidemic is growing most rapidly, particularly among the poor, is the expansion of Medicaid to low-income persons as envisioned under the 2010 Affordable Care Act. Diallo said many Southern states are not likely to opt in for that expanded coverage, potentially leaving over 17 million people, including HIV-positive people, with no access to care.

Even if Medicaid is expanded, there is a large population of undocumented persons who are not eligible for the program, she said. “It is important to stop HIV, regardless of someone’s

Donna Futterman

“If we are going to really achieve the benefits of treatment as prevention, we can’t ignore or assume we know what to do about the first step—which is addressing the gap between those who are infected and those who know,” said Donna Futterman, director of the Adolescent AIDS Program at the Albert Einstein School of Medicine in New York City.

An estimated 20-25% of Americans infected with HIV are unaware of that fact. The percentage is even higher overseas in countries hardest hit by the epidemic. Much of that is largely because HIV has been shuffled off to specialists so that the broader medical community does not have to deal with it, Futterman said. “In many ways our health care system still has not stepped up.”

“If we are ever going to get routine testing [for HIV], it is not going to be an AIDS program. It is going to be in general and routine healthcare,” she said. “In the Bronx, in South Africa, there is a tremendous amount of provider resistance to bringing HIV into their workplace.”

”Until we make HIV testing as routine as anything else in medical care, I don’t think we are going to make progress” on reaping the full benefits of treatment as prevention.

Read the story “HIV Treatment as Prevention,” by Jon Cohen in Science’s 2011 Breakthrough of the Year issue.

Learn more about the XIX International AIDS Conference, held 22-27 July in Washington, D.C.